The present invention relates to methods of compressing waveform data and more particularly, to a high-quality, low-bit-rate method of compressing such data.
It is known to perform data-compression schemes on measured data as a way of converting that data to a condition for storing it more efficiently than if it were uncompressed. The usual scenario is to design such a scheme that allows the data to be compressed for storage, and then later, as desired, to be uncompressed for use/evaluation of it.
A problem encountered when developing such a scheme is to design it in such a way that it will meet two competing goals: (1) to store the data efficiently, and (2) to store the data in a high-quality format that accommodates substantial representation of the data when it is uncompressed for later use/evaluation.
One setting where such compression schemes are useful is in connection with testing equipment that measures a periodic quantity that changes over time. Commonly, the periodic quantity is measurable via a signal which carries information representative of the quantity. Also, the periodic quantity may be associated with animate or inanimate objects.
In one example, the object is a living subject with a heart and circulatory system, and the periodic quantity is ECG-waveform data associated with that subject, i.e. the periodic electric potentials caused by heart action and occurring between different parts of the body.
Shifting from the example back to the above-referenced general setting, waveform data corresponding to the periodic quantity is obtained by plotting the instantaneous values of the periodic quantity against time. The resulting waveform data provides valuable information, and one such value is that it can be used to provide diagnostic information about the object to which it relates. Again shifting to the above example, ECG-waveform data provides information that is useful to diagnose heart disease.
In applications where waveform data is obtained electronically and where a substantial amount of such data is produced, it becomes necessary to store the data for later retrieval and use/evaluation. Again turning to the example, ECG-waveform data is commonly obtained electronically, stored in memory, and then subsequently retrieved from memory for diagnostic evaluation by health professionals.
There is a need to develop waveform-compression methods to increase waveform-data-storage efficiency and effective transmission bandwidth (the latter relating especially to bidirectionally sending such data using a communication system). In the hospital-ECG-monitoring field it is now common for remote ECG monitors to be connected to patients in their hospital rooms, and to be connected electronically to a central station monitor. There is a specific need associated with this particular application for compressing ECG-waveform data for later retrieval/use because health professionals desire to have what is known as full-disclosure archiving of such data. Full-disclosure archiving involves storing for each patient ECG-waveform data obtained in a 24-hour period.
Consistent with the need for improved data-storage efficiency, there have been many proposals for compressing waveform data. However, none of the conventional proposals has been wholly satisfactory in meeting the competing goals of (1) high compression of waveform data and (2) high quality appearance associated with a waveform reconstructed (i.e. uncompressed) from such compressed data.
Many conventional proposals are also limited because they are based on, and require identification of beats, i.e. the occurrence of a QRS complex which relates to the moment when the ventricles of the heart depolarize and the heart pumps blood through the body. Such beat-based methods require detection of each successive beat, which detection is itself complicated and potentially artifact-producing.
Accordingly, it is a principal object of the present invention to provide a waveform-data-compression method that overcomes the drawbacks of conventional methods.
Another object is to provide such a method that effects waveform-data-compression without requiring beat detection.
A still further object is to provide such method that offers increased waveform-data storage efficiency.
Yet another object is to provide such a method that provides increased effective transmission bandwidth for waveform data.
A still further object is to provide such a method that retains a desired appearance in a waveform reconstructed from a compressed version of it.